At present, the portland clinker is produced from a finely disintegrated and homogenized mixture of limestone (55-60 mass %) and phosphoric slag (40-45 mass %). The ratio of components in said mixture of raw materials is determined by the saturation coefficient of clinker (SC): ##EQU1## i.e. by the degree of saturation of SiO.sub.2 to 3CaO.SiO.sub.2.
The prepared mixture of raw materials is calcined at 1350.degree.-1450.degree. C. until the oxidized calcium is fixed completely in the minerals of portland clinker. Then the produced portland clinker is subjected to forced air or water cooling (SU, A, 507537, 299475).
However, the produced clinker contains phosphorus oxide (phosphorus pentoxide P.sub.2 O.sub.5) in the form of a solid solution in clinker minerals which retards the setting time of cement and reduces compression strength from 15 to 20 MPa at the initial periods of hardening. This, then, leads to swelling and peeling of the exposed surfaces of fresh molded products in the course of their steaming.
There is another known method for production of portland clinker from a ground and homogenized mixture of crudes containing limestone, phosphoric slag and an aluminosilicate component by calcining (SU, A, 876580).
This partially reduces the swelling and peeling of fresh products in the course of steaming and raises their strength in the course of the first three days to 23 MPa.
Known in the prior art is a method for the production of portland clinker wherein a low-oxidizing medium at 1,450.degree. C. a mixture of crudes containing limestone, phosphoric slag and cinder produced by calcining of pyrite, is calcined at a following ratio of components, wt %;
______________________________________ limestone 53-58.7 phosphoric slag 36-44 cinder 2.1-6.6 ______________________________________
(S.A. Slobodchikova "Investigating a possibility of producing high-grade clinker from phosphorus-containing slags", a thesis, Cement Research Institute, 1964).
A disadvantage of this method lies in a low strength of cement after steaming (10-20 MPa) and destructive processes manifested by swelling and peeling of exposed surfaces after steaming of fresh molded products.